The decomposition kinetics of a series of thiourea dioxides has been studied in alkaline media. In aerobic conditions the decomposition is characterized by an induction period, which is followed by the formation of dithionite, S 2 O 4 2-. The rates of consumption of the thiourea dioxide and the formation of dithionite follow zero-order kinetics. No dithionite is formed in anaerobic conditions, although the thiourea dioxides can still rapidly decompose in the absence of oxygen to give sulfite and a urea as the decomposition products. No dithionite is formed until all the dioxygen in solution has been consumed, and hence the induction time is determined by the initial oxygen concentration in solution. A comprehensive mechanism that can adequately explain the decomposition is proposed in which the initial step is the cleavage of the C-S bond to give a urea residue and the sulfoxylate ion, SO 2 2-. The sulfoxylate ion is next rapidly oxidized by oxygen to give the anion radical, SO 2 -, which is the precursor to the formation of dithionite via a rapid equilibrium. In aerobic environments the sufoxylate ion can produce the highly tissue-damaging series of reactive oxygen species superoxide, peroxide, and hydroxyl radical. These species could be responsible for the inherent toxicities associated with thioureas.
The mtDNA variation of 198 Aleuts, as well as North American and Asian populations drawn from the literature, were analyzed to reconstruct the Aleuts' genetic prehistory and to investigate their role in the peopling of the Circumarctic region. From median-joining network analysis, three star-like clusters were identified in the Aleuts within the following subhaplogroups: A3, A7 (an Aleut-specific subclade of A3), and D2. Mismatch analyses, neutrality test scores, and coalescent time estimates for these three components provided evidence of two expansion events, one occurring at approximately 19,900 B.P. and the other at 5,400 B.P. Based on these findings and evidence from the archaeological data, four general models for the genetic prehistory of the Aleutian Island chain are proposed: 1) biological continuity involving a kin-structured peopling of the archipelago; 2) intrusion and expansion of a non-native biface-producing population dominated by subhaplogroup D2; 3) amalgamation of Arctic Small Tool tradition peoples characterized by D2 with an older Anangula substratum; and 4) biological continuity with significant gene flow from neighboring populations of the Alaskan mainland and Kodiak Island. The Aleut mtDNAs are consistent with the Circumarctic pattern by the fixation of A3 and D2, and the exhibition of depressed diversity levels relative to Amerind and Siberian groups. The results of this study indicate a broad postglacial reexpansion of Na-Dene and Esko-Aleuts from reduced populations within northern North America, with D2 representing a later infusion of Siberian mtDNAs into the Beringian gene pool.
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